The present invention relates to an improvement of a pressure oil lead-in portion for feeding pressure oil, at the time of braking, into a cylinder portion provided in a caliper, that is, a body of a hydraulic apparatus, for example, a disc brake for braking a vehicle, thereby expecting to prevent oil leakage due to rust from occurring.
In a disc brake used for braking a vehicle, a pair of pads are provided so as to sandwich a rotor which rotates together with a vehicle wheel. The pads in pair are caused to press the opposite side surfaces of the rotor by a piston pushed out by oil pressure at the time of braking.
FIG. 4 shows an example of an pressure oil lead-in portion for feeding an oil pressure generated by depression of a braking pedal into a caliper having a piston therein.
A caliper 1 made of aluminum (the term "aluminum" means aluminum or an aluminum alloy, and this applies to the whole of this specification) has a cylinder portion 18 therein. An oil passage hole 2 for connecting the cylinder portion 18 to the outside of the caliper 1 is formed in a side wall of the caliper 1. A female screw 3 is formed in an inner circumferential surface of the oil passage hole 2. Further, a seat portion 4 is formed at a circumferential portion of the oil passage hole 2 on the outer side surface of the caliper 1. The seat portion 4 is finished to have a mirror surface. An annular union 6 is provided at an end of a pressure oil feeding/discharging pipe 5 communicating with a pressure oil feeding means such as a master cylinder or the like. As shown in FIG. 5, an end of a path 7 communicating with the pressure oil feeding/discharging pipe 5 is opened in the inner circumferential surface of the union 6.
Such a union 6 is fixed to the seat portion 4 by a union bolt 8 engaging with the female screw 3 on the inner circumferential surface of the oil passage hole 2. The union bolt 8 is constituted by a rod portion 9 having a diameter smaller than an inner diameter of the union 6 and a head portion 10 having a diameter larger than the inner diameter of the union 6. An oil path 11 is formed inside the rod portion 9 so that the path 11 has opposite ends opened in a middle portion side surface of the rod portion 9 and in an end surface of the same, respectively. Further, copper packings 12 and 12 are sandwiched between the seat portion 4 and the union 6 and between the union 6 and the head portion 10 of the union bolt 8 respectively to thereby prevent the pressure oil from leaking through the respective gaps.
In braking, pressure oil fed inside the union from the pressure oil feeding/discharging pipe 5 through the oil path 7 is further fed into the cylinder portion 18 of the caliper 4 through the oil path 11 and the oil passage hole 2 to thereby push out the piston fitted on the cylinder portion 18 to thereby perform braking.
When the union bolt 8 is firmly screwed into the female screw 3, the union 6 is prevented from rotating by the engagement between the pressure oil feeding/discharging pipe 5 and a notch 14 formed in a wall portion 13 at an end portion of the seat portion 4 in the case of the structure shown in FIG. 4, and by the engagement between a pin 15 fixed to a top end portion of the union 6 and an engagement hole 16 formed in an outer side surface of the caliper 1 in the case of the structure shown in FIG. 5.
There are however following problems to be solved in the conventional pressure oil lead-in portion of the disc brake having a configuration so as to operate as described above.
That is, since aluminum and copper which are different in electric potential from each other form a set of battery under the existence of water, if water drops such as rain water or the like adhere to the inside of a fine gap 17 existing between the seat portion 4 and the union 6, corrosion due to an oxidation reaction is generated on the caliper 1 made of aluminum which is base metal.
In the case where such corrosion of the caliper 1 is left as it is, the cylinder portion 18 provided in the caliper 1 becomes communicated with outside so that it becomes impossible to heighten the inside pressure of the cylinder 18 and it becomes therefore impossible to perform braking.